Nucleoside diphosphate kinase (EC 2.7.4.6.) (NDP kinase) is required for the phosphorylation of ribo- and deoxyribo- nucleoside diphosphates to their corresponding triphosphates, thereby providing building blocks for the biosynthesis of DNA, RNA and other cellular components. Recent studies suggest that the NDP kinase gene functions are also involved in development, oncogenesis, and in interaction with the GTP-binding protein family in various organisms. Although these results are intriguing, most such studies are still preliminary. We propose to use the budding yeast Saccharomyces cerevisiae as a model to investigate the gene functions of NDP kinase within the cell. The initial goal of this proposal is to investigate the interaction of NDP kinase and dTMP kinase (and other nucleotide kinases) in order to delineate their interacting domain(s) and to uncover the biological significance of such interaction. The second goal is to identify an array of thus far unknown components which coordinate with NDP kinase, so as to elucidate NDK1's putative linked pathways. The third goal is to identify and characterize a putative second NDP kinase (tentatively designated as NDP kinase-II) in yeast. We expect that the investigation of the yeast NDK1 gene and its related protein component(s) will lead to an understanding of several important biological functions in yeast; extension beyond the relatively well-defined yeast organisms, may allow us to better understand the diverse functions of NDP kinase in other eukaryotes.